分享一点关于 PG 的小知识

xisi — Thu, 20 Nov 2014 15:18:27 +0800

在我们的业务量不断增长中需要我们谨慎的操作数据库

分享一点心得

一。碰到需要添加索引，需要用到 CONCURRENTLY，可以避免锁的问题

如 create index CONCURRENTLY idx_table_names_titem_uid on table_names(titem_uid)

文档可以见： http://www.postgresql.org/docs/9.1/static/sql-createindex.html

二。有时我们会去执行一些费时耗数据库的任务有时会发现某一个任务还在暗地里执行着需要我们手动的关闭该任务

如果你是 kill 对应的 pid，你很有可能会出现数据库的问题保险的做法是用 PG_CANCEL_BACKEND

通过如下查找对应的 PID

select pid, trim(starttime) as start, duration, trim(user_name) as user,substring (query,1,40) as querytxt from stv_recents where status = 'Running';

查看 select pg_cancel_backend(802);

通过如下杀掉任务

pg_cancel_backend( pid )

可以见文档： http://docs.aws.amazon.com/redshift/latest/dg/PG_CANCEL_BACKEND.html

使用 accepts_nested_attributes_for 是不是可以解决问卷调查的模型实现

xisi — Wed, 18 Sep 2013 17:06:12 +0800

class Category
  include Mongoid::Document
  include Mongoid::Paperclip
  include Mongoid::Tree
  include Mongoid::Tree::Ordering

  field :title, :type => String
  field :desc,  :type => String, :default => ''

  has_many :books, :autosave => true

  has_mongoid_attached_file :img
  attr_accessible :img, :books_attributes, :title, :desc
  accepts_nested_attributes_for :books, :allow_destroy => true
end

.page-model-form
  = form_for @category do |f|
    .field.need
      %label title
      =f.text_field :title

    .field
      %label desc
      =f.text_field :desc

    .feild
      %label img
      =f.file_field :img

    .field.books
      .book
        - book = @category.books.build

        = f.fields_for :books, book do |book_form|
          %label name
          =book_form.text_field :name

          %label desc
          =book_form.text_field :desc

    .field
      =f.submit

一份问卷中，有多道题的模型

xisi (MenDD)

分享一点关于 PG 的小知识

使用 accepts_nested_attributes_for 是不是可以解决问卷调查的模型实现